Water vortex exhibit repair gives a look at the bearing and gasket design

[Ben Krasnow’s] water vortex machine has been an exhibit in the lobby of the San Jose City Hall for quite some time now. Unfortuantely he recently had to perform some repair work on it due to the parts inside the water chamber rusting.

This is the same water vortex that we saw about a year ago. It uses a power drill to drive an impeller at the bottom of a water column to produce the vortex. That impeller was made from painted steel and after being submerged for eight months it began rusting, which discolored the water. [Ben’s] repair process, which you can watch after the break, replaces the shaft and the impeller. He reused a plastic PC cooling fan as the new impeller. The replacement shaft is stainless steel, as is all of the mounting hardware that will be in contact with water. But for us, the most interesting part of the repair is his explanation of the shaft gasket and bearings. Two thrust bearings and two radial bearings ensure that the shaft cannot move axially, which would cause a problem with the gasket. He had intended to swap out the oil seal for an all Teflon seal but the machined acrylic wasn’t conducive to the part swap. Instead, he replaced it with the same type of gasket, but bolstered the new one with some silicone to stave off corrosion.

He says the original purpose was get someone interested in mechanical engineering or something. It’s a good idea, but I wonder if the torque required to stir the water at that speed is greater than the force of the magnet small enough to overcome the friction against the bottom surface as it is pulled down.

Strong magnets and teflon base as noted would work fine :) You don’t really need super-fast spinup time, unless that’s the point of this demonstration… A normal magnetic stirrer would work fine, give a minute of spinup time to get the whirlpool going.

You can get higher torque mag drive units. They are common on chemical pumps that will dissolve or react with stainless steel.

But why use components whose inherent construction is not suitable for the environment in which it is expected to operate? A la steel in water instead of stainless. Why not start with stainless rather than have to fix it all later?

What astounds me about this story is that someone would build a museum exhibit demonstrating a water effect and _NOT_ use stainless or long-life materials. No wonder so many kids who push demo buttons at museums are left disappointed when nothing happens.

came here to say this: What kind of hack makes a permanently water-submerged assembly out of painted plain steel? Seriously? It wouldn’t even enter into my mind to make it out of anything but stainless steel or titanium.